Many Antibiotics Are Headed Straight for Your Gut—And That Could Be Making You Fat

We need them to treat disease, but these drugs might also be causing all sorts of collateral damage.
Take one daily. Possible side effects may include gaining weight. (John Foxx/Getty)
Aug 26, 2012
A former Gourmet staffer, Lawrence enjoys writing about design, food, travel, and lots of other stuff.

“Antibiotics may plump up cows, pigs, chickens, mice and humans alike,” reports Science News. “For decades, low doses of antibiotics have been given to livestock to make the animals grow and bulk up faster, but no one really knew how the drugs promoted growth. Now, researchers led by microbiologist Martin Blaser at the New York University School of Medicine report online August 22 in Nature that antibiotics alter the mix of bacteria in the intestines of mice and cause the rodents to build up more fat than normal.”

The article went on to explain, “Although antibiotics are meant to kill bacteria, the researchers found that the total number of bacteria in the mice’s guts didn’t change. But the mix of the microbes did....Gut microbes in antibiotic-ingesting mice produced more short-chain fatty acids, a type of fat that cells use for energy. ‘Essentially you’re getting more fuel from the same amount of starting material,’ ” said study coauthor Illseung Cho, a gastroenterologist at NYU.

Commenting on Cho’s observation, Mother Jones said, “That last statement is key: It means that antibiotics give meat producers more bang for every buck of feed. But given that the practice of dosing animals with antibiotics is quite likely generating antibiotic-resistant pathogens that infect people, the real price of that benefit seems steep. How much are we willing to endanger public health in order to generate an abundance of cheap meat?”

MORE: Human-Animal Diseases Kill 2.2 Million People a Year

Science News also noted that, “In a separate study, published online August 21 in the International Journal of Obesity, Blaser’s group found a link between antibiotic use in babies younger than six months old and being overweight at age three. Together, the [two] studies suggest that medications that alter the mix of friendly bacteria in the gut may have lasting effects on body weight.”

Blaser has been studying the possible unintended effects of antibiotics for awhile. The Los Angeles Times quoted him in 2011 saying that, “Antibiotics kill the bacteria we do want, as well as those we don’t...Sometimes, our friendly flora never fully recover.”

The Times observed, “in many respects, an antibiotic targets a particular disease the way a nuclear bomb targets a criminal, causing much collateral damage to things you’d rather not destroy...And that can leave us more susceptible to various kinds of diseases, especially considering that the typical American is exposed to 10 to 20 antibiotics during childhood alone.”

And a study published in 2010 in the journal Proceedings of the National Academy of Sciences of the United States of America also offered a cautionary view, stating, “The use of broad-spectrum antibiotics to treat acute infectious disease will undoubtedly continue because of immediate, undeniable benefits for human health...however, there would remain a less obvious but perhaps more important risk to antibiotic use. The antimicrobial agents that we deploy against pathogens also disrupt coevolved microbial communities that are integral to human health.”

In summary, Science News noted, “While the study may help explain how chronic exposure to antibiotics boosts growth in animals, it doesn’t necessarily mean that the medicines’ use for short stints in people can be blamed for weight gain.” The story quotes David Relman, a microbiologist at Stanford University, as saying, “I think the work described in the Nature manuscript is provocative and intriguing, but I would not jump to conclusions about mechanisms and about the translatability of the work to children.” 

I’m no microbiologist, but I’m definitely intrigued.

Do you think antibiotics are over-prescribed to both people and animals? Let us know in the comments.

Lawrence Karol is a writer and editor who lives with his dog, Mike. He is a former Gourmet staffer and enjoys writing about design, food, travel and lots of other stuff. @WriteEditDream | Email Lawrence |

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